Leacture three limb bud formation Flashcards

1
Q

what are the three parts of a limb (p to D)

A

stylopod, zeygopod, autopod

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2
Q

when does limb foration start in the chick

A

3 days

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3
Q

when does kimb formation start in the mouse and when is it formed

A

10 daysto 14 days

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4
Q

where doe the limb bud form

A

junctin between the dorsal and ventral ecotderm

in distinct position along the AP axis

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5
Q

what experiment shows the AP axis is established very early

A

take presomiic mesoderm and graft back in incerted = somites form in reverse order
this shows cells have been predetermined with their positional identity

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6
Q

how is fgf8 expressed

A

gradientwith highest at the posterior

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7
Q

what is the expression attern of retinoic acid

A

is highest in the mid trunk of the embryo and declines both posteriorally and anteriorally

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8
Q

what is the role of the fgf8 and RA gradients

A

give positional identity to cells along the AP axis

an address of where they are on it

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9
Q

what other signally are also important in establishing the AP axis

A

WNts and BMPS expressed in posterior (WNT and BMPantagonists expressed in anterior)

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10
Q

what is th eoutcome of the signalling gradients

A

RA/WNT3a and fgf8 activate TF (cdcxs) these then activate Hox genes
hox genes inv in AP patterning

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11
Q

what are properties of HOx genes

A

homeotic TFs
evolutionary conserved
show colinearity
in their order along the chromosome and spatial/temporal pattern along the AP axis

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12
Q

where are 3’ hox genes expressed

A

at the anterior

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13
Q

what do the expression pattern of Hoxb genes show

A

shows anterior borders are distinct whilst posterior are not

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14
Q

how does hox expression explain the difference in the number of cervical vertebrae on the mouse

A

the chick has twice as many as mouse

has a bigger hox 5 expression (=hox5/6 boundary is change in the type of rib)

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15
Q

what does hox expression in the snake show

A

doesnt allow for limbs
as norm region anterior to hoxc6 becomes forelimb
in snake hoxc6 expressed thoroughout - no anterior region of its expression = no limb
expansion of hoxc6 and hoc8 expression correlates with the expasion of thoracic identitiy of skeleton as no act of necessary signalling pathways

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16
Q

what is the role of fgf10 and how was this shown

A

in lpm
initiates limb bud formation
is expressed in the correct areas jus tprior to fomation
ectopic expression induces and ectopic limb
ko = no limb = is necessary

17
Q

what is the TF that activates fgf10

18
Q

what controls the position of fgf10

A

tbx5 activation
tbx5 expression is activated by the rostral hox code (hox4/5)
and tbx5 expression is repressed by caudal hox code expression

19
Q

where does the fgf10/hox/tbx signalling occur

A

in the lateral plate mesoderm

20
Q

what does fgf10 induce in the ectoderm of the limb bud

A

fgf8 expression

21
Q

what TF is expressed in the forelimb bud

22
Q

what TF are expressed in the hindlimb bud

A

Tbx4 and Pitx1

23
Q

what does inducing an ectopic limb etween the two normal limb buds with a fgf10 bead show

A

in the ectopic limb there is chimeric expression of the tbx gnees = this is consistent with these genes being progeitors for the HL and FL

24
Q

in the chick what is the consequence of tbx4 overexpression and what is the consequence of tbx5 overexpression

A

tbx4 takes on HL identity (wt= FL)

tbx5 takes on FL identity (wt= HL)

25
what do the overexpression expreiments of tbx genes in the chick show
confirms their role in the FL/HL identitiy
26
what occurs in the mouse if KO the tbx genes
tbx4 - defect in hl | tbx5 - defect in fl
27
what do conditional ko and rescue of tbx4 show
(KO tbx5 then put in tbx4) shows that tbx4 is not sufficient to give hindlimb identity in the mouse = ptype still resemble FL
28
what do experiments with pitx1 show
misexpress in fl gives more hl id ko = loss of hl feature when do condtional ko of tbx5 then save with pitx1 = no limb = not sufficient conditonal ko of tbx5 then rescue with tbx4 and pitx1 = partial hl therefore both imp for fl id
29
what signalling pathway group do fgf belong to ?
tyrosine receptor kinases